Recorded October 11th, 2011
Presented by RTP Company
Modified and reinforced plastics provide increased mechanical performance and allow plastics to be used to solve the unique and challenging material requirements of today’s leading product development efforts. See how structural compounds could be the key to your next successful application by joining Karl Hoppe, Product Development Engineer at custom compounder RTP Company, as he shows you how various additives can be used to boost performance. Karl will cover all the possible options including stabilizers and impact modifiers, particulate fillers such as minerals, reinforcements like glass and carbon fiber, and metal replacing long fiber composites.
Questions and Answers
Q: I understand that the distribution and disposition of the filler can be also influential on the mechanical properties. Until what level?
A: The level of dispersion and distribution required of an additive to affect mechanical properties is going to be different for each and every additive. If we try to get too much dispersion and distribution of a reinforcing fiber, we may reduce its length (and therefore also its aspect ratio) and thereby reduce the level of reinforcement that it provides. On the other hand, you will want to get high levels of dispersion of fillers that already have low aspect ratios. Undispersed clumps of mineral, for example, may act as stress concentrators that could have a negative effect on your properties. So as you can see it is different for each type of additive technology.
Q: You have not touched the issue of compatibilizing agents between the fillers whatever the filler type and the compound. Could you explain shortly the importance of these components in polymer applications?
A: The interface between a filler and the resin it is dispersed in is pretty science. Yet there are additives and surface treatments that are known to improve compatibility between the polymer and the additive. In some cases they are surface treatments that our suppliers put onto the fibers – sizing on glass fibers, for example. In other cases there are additives that we can include in the formula. An industry standard would be using maleic anhydride grafted polypropylene as a chemical coupling agent to improve glass reinforced properties. In some cases it’s knowing what additives to use to enhance your compound; in other cases it’s selecting the right fiber or filler itself (with their surface treatments) that gives you the best combination of properties.
Q: Do you have modifiers and or fillers to that would aid in thermal conductivity?
A: We do have some thermally conductive compounds. Dr. Joel Bell discussed that in his IDES Webinar from February, 2011 on conductive plastics. You can also view product information on RTP Company’s website to see what is available.
Q: Does glass content have impact in chemical resistance?
A: Generally glass contact will not have a significant effect on the chemical resistance of a compound. That’s usually considered a resin-specific property. However, if you have very caustic chemicals used with a compound that has a very high level of glass fiber (where some will inevitably be on the surface), this should be taken into consideration. Also, if the fibers are increasing the level of molded-in stress it could also reduce chemical resistance, since chemicals have a greater effect on the areas of high stress in a molded composite.
Q: What is the smallest size of glass beads you have available?
A: Glass beads come in many different sizes. As you may have noticed I referenced Potters, Inc. as a supplier who offered to allow us to use the SEM photo of glass beads (and we thank them for that). You may want to look at Potters’ product line to see what is generally available.
Q: Is the size of glass beads affect strength?
A: There may be some small changes in the mechanical properties from what set of glass beads to another, but the aspect ratio is still 1 and it will not be a reinforcing additive. They will all reduce strength and impact resistance while increasing stiffness.
Q: To clarify, does the compressive and tensile plastic properties get modified equally?
A: Compressive properties are sometimes challenging to test on thermoplastics (see ASTM D695), but as a general rule changes in compressive properties mirror changes in tensile properties. “Equally” is a strong word. “Mirror” is a bit safer.
Q: Do modifiers and/or beads and fibers affect the plastic anisotropy of the compounds?
A: Modifiers generally don’t affect anisotropy unless they impart a high level of crystallinity. The level of anisotropy that a fiber or filler creates is based on its aspect ratio. Generally the higher the aspect ratio the more anisotropy you realize. There tends to be a limit here – perhaps a secondary critical fiber length where a glass fiber can begin to curl (like with our VLF products) where anisotropy can become slightly less severe
Q: Is there some ecological restriction related to combine different material and fiber/Modifiers.
A: There generally aren’t any regulatory issues that affect combinations – regulatory issues generally center around the additives or resins themselves (RoHS or REACH, for example). There are some chemical incompatibilities to recognize however – like the fact that glass fiber cannot be used as a reinforcement in PVDF – it can become explosive!
Q: What is the guideline for gate location for glass filled material to minimize warpage. What is the ideal type of gate (edge, fan)?
A: We have a whole team of experts that are more qualified to answer this question than I (I’m more on the formulation side). You might find some general rules that are helpful by requesting our Guidelines for Plastic Design – which can be requested here. Otherwise – you’ll often find that generalities fall somewhat short when you take into account the specific requirements, materials, and design you’re working with. You can interface with your local Sales Engineer from RTP Company to get the right people involved up front.
Q: Does the effect of aspect ratio on mechanical properties significantly depend on the orientation of the fillers?
A: There is definitely an orientation effect. You will have higher mechanical properties (in general) in the direction of flow compared to the transverse direction. You might find some of this information helpful.
Q: Do long fibers cause problems at the gate?
A: Generally not. You can review our Long Fiber Compounds Molding Guidelines to handle some basic Long Fiber design questions up front, and contact your local Sales Engineer if you need additional help from our Technical Services group.
Q: Can you recommend blends for all-polymer hip or knee replacements? Friction and wear of polymer against polymer, as well as biocompatibility are important factors.
A: RTP Company’s policy is to not supply materials for applications that will be permanently implanted in the human body. For applications that will have brief or temporary contact (<30 days) we do supply materials under a special agreement. Our involvement with orthopedics is generally surgical tools, sizers, etc. Not the implanted components themselves.
Q: What modifiers do you recommend for wear resistance?
A: A nice summary can be found on RTP Company’s website.
Q: Are all blended materials RoHS compliant?
A: RoHS compliance is a property that we need to know up front during development. It usually isn’t an issue but does become a factor when formulating flame retardant materials. More information is available in this webinar on Flame Retardant Plastics.
Q: Is there an alternative to the burn-off test to determine fiber size and distribution for carbon fiber reinforced parts?
A: You could do some acid digestion of the resin or we have occasionally tried what’s considered a “microwave ash” sort of test. These methods have had mixed results.
Q: Does Aspect Ratio change after injection molding
A: Well, Aspect Ratio never gets bigger! The molding process is a shear-intensive process that can break down the length of the fibers. Care needs to be taken when molding to try to reduce shear wherever possible (mold design, gate design, screw selection, back pressure, screw speed, etc.).
Q: How do modifiers impact recyclability of a resin? May they be mixed with pure resins?
A: In some cases yes, in some cases no. Generally speaking the public recycling streams in today’s world are pretty narrow. If you have a steady recycling stream all thermoplastics are reprocessable.
Q: Do these modifiers, filler/fibers and long glass, not lend themselves to a part that needs to be optically clear?
A: In the vast majority of cases these additives will render the resin translucent at best and many times opaque.
Q: When do we use beads or Talc in applications ?
A: As a general rule of thumb we probably see (and use) minerals in semicrystalline resins and glass beads in amorphous resins, though that’s only a general rule of thumb. It ultimately depends on comparative data – we’ve looked at the mechanical property performance of many combinations of materials so we can offer the best solution possible.
Q: Do you also guide with molding conditions of such specialized plastics?
A: Yes. We have engineers and technical service personal available to assist with this, including mold flow analysis, and FEA.
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